1. Field of the Disclosure
The present disclosure relates to an organic light emitting diode display device, and more particularly, to an organic light emitting diode display device and a method of driving the same, where the lifetime of the display device may be improved by compensating for degradation and non-uniformity properties of a transistor in the display device.
2. Discussion of the Related Art
FIG. 1 is a schematic drawing illustrating an equivalent circuit of a pixel of an organic light emitting diode display device, and FIG. 2 is a timing chart of the control signals of an organic light emitting diode display device.
As shown in FIG. 1, in the pixel of the ordinary organic light emitting diode display device, first and second transistors (T1 and T2), a driving transistor (Tdr), a light emitting control transistor Tem, first and second capacitors C1 and C2, and an organic light emitting diode (OLED) may be formed. The transistors (T1, T2, Tdr and Tem) may be PMOS type transistors.
The first transistor (T1) has a drain electrode where a data voltage (Vdata) is supplied, a gate electrode where a select signal is supplied, and a source electrode which is connected to the first capacitor (C1).
The second transistor (T2) has a drain electrode which is connected to the second capacitor (C2), a gate electrode where a control signal is supplied, and a source electrode connected to a source electrode of the light emitting control transistor (Tem).
The light emitting control transistor (Tem) has a drain electrode which is connected to a source electrode of the driving transistor (Tdr), a gate electrode where a light emitting control signal is supplied, and a source electrode connected to the organic light emitting diode (OLED).
The light emitting control transistor may sense a threshold voltage of the driving transistor (Tdr) and may prevent the organic light emitting diode (OLED) from emitting light while the data voltage (Vdata) is supplied.
The driving transistor has a drain electrode connected to the second capacitor (C2), a gate electrode connected to the first capacitor (C1), and a source electrode connected to the source electrode of the second transistor (T2).
In other words, in the organic light emitting diode display device of the related art, the gate and drain electrodes of the driving transistor (Tdr) are connected with each other to complete a diode structure.
The driving transistor (Tdr) functions as a current source to let current flow to the organic light emitting diode (OLED), allowing the organic light emitting diode (OLED) to emit light.
The strength of the light emitted from the organic light emitting diode (OLED) is proportional to the amount of current flow through the organic light emitting diode (OLED). The amount of current flow to the organic light emitting diode (OLED) may be proportional to the strength of the data voltage (Vdata) applied to the gate electrode of the driving transistor (Tdr).
Therefore, the organic light emitting diode display device can display images by applying various data voltages (Vdata) to pixels to show different tone wedges.
To drive pixels, there are typically a plurality of control signals such as a control signal (Control), a light emitting control signal (Em), and/or a select signal (Select).
As shown in FIG. 2, the data voltage (Vdata), the control signal (Control), and the select signal (Select) may maintain the voltage level at a low level (Low) for a relatively short time, and for the rest of the time (which is relatively long) the select signal (Select) may maintain the voltage level at a high level (High). This forms a pulse shape.
However, in embodiments where the first and second transistors (T1 and T2), the driving transistor (Tdr), and the light emitting control transistor (Tem) are NMOS-type transistors, the above explanations should be reversed.
For example, in embodiments where the above-noted transistors are NMOS-type transistors, the first and second transistors (T1 and T2) maintain a turn-on state (Turn-On) while a low level select signal (Select) and low level control signal (Control) are respectively applied to these transistors.
Meanwhile, the voltage level of the light emitting control signal (Em) is maintained at a high level (High) for a short time, and maintained at a low level (Low) for a long time. This forms a pulse shape.
In other words, the light emitting control transistor (Tem) maintains a turn-on state for a long time while a low level voltage (Low) is applied via the light emitting control signal (Em).
If the light emitting control transistor (Tem) maintains a turn-on state for a long time, the transistor may become degraded and the quality of the display may worsen.
Also, because the gate and drain electrodes of the driving transistor (Tdr) are connected to each other to form a diode structure, it is impossible to sense a positive threshold voltage.
Accordingly, there occurs a problem that the amount of current flowing through the organic light emitting diode (OLED) varies depending on a deviation of positive threshold voltage.